Author: Ane Lasa
Requested Type: Pre-Selected Invited
Submitted: 2018-03-01 09:43:03
Co-authors: T. Younkin, S. Blondel, G. Shaw, B.D. Wirth, D.L. Green, J.M. Canik, J. Drobny, D. Curreli, M.J. Baldwin, R.P. Doerner
University of Tennessee
1412 Circle Dr
Knoxville, TN 37916
Plasma-surface interactions (PSI) span diverse physical processes and decades of time and length scales (ps–s and Å–m). Correspondingly, comprehensive modeling of PSI must accurately target each scale and mechanism.
We describe coupling of high fidelity plasma and material models, within the Integrated Plasma Simulator (IPS) framework, to predict the evolution of tungsten (W) surfaces exposed mixed deuterium (D) - helium (He) plasmas. In our workflow, plasma characteristics are measured experimentally or calculated by SOLPS. Our new global impurity transport code GITR models the migration and re-deposition of W particles eroded from the surface based on plasma parameters. The binary collision code Fractal-TRIDYN (F-TRIDYN) calculates the energy and angular distributions and rates of sputtered particles, accounting for ion impact energy, angle and surface roughness. It also computes the ion implantation profile for a given surface composition, needed by our continuum based cluster dynamics code, Xolotl. Xolotl predicts the sub-surface evolution of implanted species, gas retention and changes in the surface height. As surface composition evolves in Xolotl, F-TRIDYN updates the sputtering rates and implantation profiles.
We have benchmarked the coupled PSI modeling workflow to dedicated experiments in the linear plasma device PISCES, with samples exposed to mixed D-He plasmas and biased to 250V to ensure observable erosion yields (O(10^-3)). We evaluate the sub-surface gas evolution, W erosion, transport and re-deposition, along with changes in surface morphology. Variations in exposure conditions of flux (0.5 – 4.0e18 cm-2s-1), fluence (0.5 – 1.0e22 cm-2), and plasma composition (100%D – 100%He) are also assessed. The predictions of W mass loss and re-deposition by GITR are consistent with experiments (within ~30%). We also discuss the comparison of modeling predictions for surface morphology and sub-surface composition, to experimental observations.